1. Field of the Invention
The present invention relates to an ink jet printer, and, more particularly, to a frame system for an ink jet printer that provides a substantially uniform printhead to print media gap throughout a print zone associated with the ink jet printer.
2. Description of the Related Art
In a typical ink jet printer having a reciprocating printhead, a printhead carriage carrying the printhead is supported by a pair of carrier guide rods which are positioned substantially traverse to a print media path. As a sheet of print media is transported in an indexed manner under the printhead, the printhead is scanned in a reciprocating manner across the width of an image area on the sheet of print media, wherein the path of the reciprocating printhead defines a print zone. A platen is provided opposite to the printhead for contacting the non-printed side of the print media and, in part, defines the distance between the printhead and the sheet of print media.
One important parameter associated with an ink jet printer is the gap between the plane of the nozzle plate of the printhead and the plane of the print media on which the ink expelled from the nozzle plate is deposited. As the gap becomes wider, the error in dot placement increases. The limits on the low end of the gap range is defined by the point at which the printhead actually contacts the media, thereby causing smearing of the freshly deposited ink. In addition, such contact with the print media can result in damage to the printhead such as, for example, by clogging the nozzles of the nozzle plate of the printhead. Thus, it is desirable in a high quality ink jet printer design to control the printhead to print media gap to a minimum value without permitting contact between the printhead and the print media. However, any variation in the parallelism between the two carrier guide rods, and any variation between the parallelism of the platen with respect to the two carrier guide rods, results in variations in the printhead to print media gap along the extent of the print zone.
What is needed in the art is a frame system for an ink jet printer that provides for a substantially uniform and adjustable printhead to platen gap throughout the print zone, and in turn provides for a substantially uniform printhead to print media gap throughout the print zone.
The present invention provides a frame system for an ink jet printer that provides for a substantially uniform and adjustable printhead to platen gap throughout the print zone, and in turn provides for a substantially uniform printhead to print media gap throughout the print zone.
The invention comprises, in one form thereof, an ink jet printer having a print zone defined by the travel of a printhead, having a media path defined to extend through the print zone and having a media feed direction. The ink jet printer includes a printer frame, and a first guide rod mounted to printer frame. A platen having a media carrying side is positioned to face the printhead, and the media carrying side is positioned along the media path. The platen has a first end located on a first side of the media path and a second end located on a second side of the media path opposite to the first side of the media path. A first stop mechanism is attached to the printer frame and a second stop mechanism is attached to the printer frame, the second stop mechanism being spaced apart from the first stop mechanism. A first pivot plate is attached to the first end of the platen, the first pivot plate including a first pivot member and a first stop surface, the first pivot plate being slideably coupled to the printer frame. A second pivot plate is attached to the second end of the platen, the second pivot plate including a second pivot member and a second stop surface, the second pivot plate being slideably coupled to the printer frame. A biasing unit provides a biasing force to position and hold the first pivot member and the second pivot member in contact with a surface of the first guide rod, to position and hold the first stop surface in contact with the first stop mechanism and to position and hold the second stop surface in contact with the second stop mechanism.
According to one method of the invention, substantially uniform spacing is provided between a printhead and a platen throughout a print zone associated with the printhead in an ink jet printer, the ink jet printer including a printer frame and the platen being slideably coupled to the printer frame. The method includes the steps of providing a first carrier guide rod attached to the printer frame; providing a second carrier guide rod having at least one end adjustably attached to the printer frame; adjusting a position of the second carrier guide rod to provide parallelism between the first carrier guide rod and the second carrier guide rod; and biasing the platen to a position relative to a position of at least one of the first carrier guide rod and the second carrier guide rod.
In preferred embodiments, for example, the first guide rod is fixedly attached to the printer frame, such as for example, by welding the first guide rod to the printer frame.
An advantage of the present invention is that the relationship of the printhead to the surface of the media in the print zone can be controlled to minimize the printhead to print media gap.
Another advantage of the present invention is that a robust printer frame structure is provided that minimizes the twist of the carrier during printing and resists the adverse affects of external forces acting on the printer frame that would twist the carrier guide rods out of parallel.
Yet another advantage is that the gap between the printhead and the platen is maintained substantially uniform throughout the extent of the print zone, and as a result, the gap between the printhead and the print media is maintained substantially uniform throughout the extent of the print zone.
Yet another advantage is that the invention ensures perpendicularity between the media path and the printhead scan path.